The present invention relates to cathodic protection of a metallic structure in contact with the earth from corrosion. More particularly, the invention relates to a method of cathodically protecting such a metallic structure and to a cathodic protection system for protecting such a metallic structure. According to another aspect, the invention relates to a method of preparing a cathodic protection system.
The technique of cathodically protecting a metallic structure which is in contact with the earth basically involves applying an electrical DC voltage across the metallic structure and a grounded electrically conductive member such that the metallic structure is the cathode and the grounded conductive member is the anode. A current is established between the anode and cathode through the earth. This flow of current causes a surplus of electrons at the cathodic metallic structure which combine with positively charged hydrogen ions from the environment to form hydrogen. Thus, a hydrogen film results over the cathodic metallic structure which tends to isolate it from the environment so as to assist in preventing corrosion.
In actual practice, the electrically conductive member which serves as the anode is grounded by positioning the conductive member within a borehole in the earth, and then filling the borehole around the conductive member with a particulate, electrically conductive "backfill" material, such as coke. The backfill material provides excellent electrical contact between the surrounding earth and the anodic conductive member.
Although cathodic protection as described above has been widely employed as an effective technique to prevent corrosion, further improvement would be desirable, particularly with regard to the backfill material.